Effects of iron-deficiency anemia linger

Infants with iron-deficiency anemia may suffer long-lasting central nervous system effects even with early treatment, say researchers at the U-M and the University of Chile.

Results of a collaborative study that was presented April 28 at the 2001 Pediatric Academic Societies and American Academy of Pediatrics joint meeting found that 3- to 4-year-old children who were treated for iron-deficiency anemia in infancy show slower transmission of nerve impulses throughout the brain in both the auditory and visual systems.

This is the most direct evidence to date that iron-deficiency anemia in infancy has long-lasting effects on the developing brain, says Betsy Lozoff, director of the Center for Human Growth and Development, and professor of pediatrics and communicable diseases.

Iron deficiency is the most common nutrient deficiency in the world, and infants are one of the age groups at highest risk, Lozoff says. In the United States, iron fortification of infant formula began about 30 years ago, and iron-deficiency anemia was drastically reduced. However, 20 percent25 percent of all infants in the world have iron-deficiency anemia, and many more have iron deficiency that is not severe enough to cause anemia.

The investigators hypothesize that the differences in nerve conduction are due to problems in myelination, because iron is required for normal myelination. The myelin sheath, a casing around the nerve, allows for speedier transmission of signals from the brain to the rest of the body or from the periphery back to the brain. Without myelin, signals cannot be transmitted as efficiently. Much myelin formation takes place early in life.

The collaborative study examined 84 Chilean children41 who had iron-deficiency anemia as infants and were treated with iron, and 43 who were never anemic in infancy. All of the children were full-term babies weighing at least 6 pounds, 12 ounces. All children were from similar communities.

Chile was chosen as the study site because it was one of the few places in the world where there was a sophisticated infant neurophysiology laboratory but also a high prevalence of iron deficiency in infants, Lozoff explains. In Chile, Cecilia Algarin and Patricio Peirano of the Laboratory for Sleep and Neurobiology at the Institute of Nutrition and Food Technology, University of Chile, headed the neurophysiologic studies.

Each child was given two tests that provide measures of the integrity of sensory systems. To test the auditory system, electrodes were placed on the scalp, and small clicks were made near the ear. This test measured the time it took for the signal, prompted by the click, to go along the auditory pathway from the ear to the brain. A second, similar test was preformed to measure visually evoked potentialsthe time it took for the signal, prompted by a visual stimulus, to go from the eye to the brain.

What we found is that there are differences in latencies, Lozoff says. That means that theres slower transmission of the nervous impulse in both auditory and visual systems for children who had iron-deficiency anemia as infants.

The changes in signal transmission also could mean that other aspects of brain function dependent on normal myelination are affected. Subtle disruptions in timing could affect broader systems of development.